This invention relates to a vane type compressor for a motor vehicle air conditioning system and, more particularly, to a control of a volume of gas discharged from the compressor to save power for operating the compressor.
As one type of method of controlling the volume of gas discharged from a vane type compressor, a continuous control method has been known in which valve assemblies capable of continuously varying their respective opening degrees are respectively disposed in suction gas passages and actuated such that the opening degrees are reduced as the rotational speed of the compressor increases, for example, to thereby reduce the volume of gas discharged from the compressor. More specifically, two suction ports are provided which open in each of two working chambers, and valve assemblies are provided each of which is operable to fully open or fully close the associated suction port. In this type of compressor, one of the two suction ports opening in one of the two working chambers is closed by the associated valve assembly when the rotational speed of the compressor exceeds a predetermined value, and when a further rise in the rotational speed of the compressor results in another predetermined level being exceeded, the other suction port of the one working chamber is also closed by the associated valve assembly, so that the volume of gas discharged from the compressor can be controlled stepwise. Some disadvantages are associated with this stepwise control process. One of them is that with the degree of openings of the suction ports being limited or restricted, the gas flowing into the working chamber would be low in density and pressure as it is compressed. The result of this would be that the temperature of the gas discharged from the compressor would rise as the opening degrees of the valve assemblies drop, thereby causing durability of the compressor to be decreased.
In another known control method, inflow of gas into the plurality of working chambers of the compressor is successively blocked as the rotational speed of the compressor rises, so that the number of working chambers rendered inoperative will increase to successively reduce the volume of gas discharged from the compressor. When this control method is used, the durability of the compressor would also be lowered because the absence of gas would result in a rise in the temperature of the working chambers which are inoperative, so that a rise in the temperature of the components of the compressor would cause a shortening of their service life.